Intervertebral discs are susceptible to a variety of weaknesses and abnormalities that can affect their ability to provide support and structure. Many of the abnormalities may be the result of, for example, trauma, degenerative disc disease, or tumors, which can cause severe pain or damage to the nervous system. Also, movement of the spinal column may be significantly limited by such abnormalities. Known treatments of such abnormalities typically involve affixing screws or hooks to one or more vertebrae and connecting the screws or hooks to a rod that is aligned with the longitudinal axis of the spinal column to immobilize the spinal segments with respect to each other. Pedicle screw systems are frequently used to provide spinal fixation.
A number of pedicle screw systems are known, which share common techniques and principles of screw placement and rod attachment. Generally, bone screws are screwed into pedicles of vertebrae and coupled to at least one elongated rod. The pedicles, which consist of a strong shell of cortical bone and a core of cancellous bone, are generally used for the bone screw sites because they provide a strong point of attachment to a spine and, thereby, the greatest resistance against bone-metal junction failure. Known pedicle screw systems typically include pedicle screws and rods to stabilize adjacent spinal segments. Such systems may also include variable angled coupling caps (or heads) on the pedicle screws to allow for angular adjustment of the coupling mechanism between the rod and screws. Since pedicle size and angulation varies throughout the spinal column, several different sizes and shapes of pedicle screws are used in these systems. These systems are generally designed to provide stable and rigid structures to promote bone growth and fusion. The systems may include a pair of rods, plates, or other elongate members affixed to the pedicle screws along the longitudinal axis of the spine.
The strength and stability of a multi-rod, plate, or other elongate member assembly can be increased by intercoupling the elongate members with a cross connector that extends substantially horizontal to the longitudinal axes of the elongate members, across the spine. Due to a wide variety of factors, the elongate members are seldom geometrically aligned in clinical applications. Furthermore, typical cross connectors are inserted through either a fully open or mini-open procedure, resulting in resection of the spinal ligaments and bone. A minimally invasive connector system with at least some adjustability is needed that can accommodate for variations in geometrical alignment while minimizing damage to the supporting anatomical structures.